1. Field of the Invention
The present invention relates to a rope member including a synthetic fiber rope and a clamping member to be used for connecting or fastening the rope to an external member, an overhead door having the rope member, and a method for producing the rope member.
2. Description of the Related Art
In recent years, the improvement has been made for the method of producing synthetic fibers, and it is possible to produce extremely fine fiber strands. By twisting the fiber strands in various shapes, produced are synthetic fiber ropes which are superior or no way inferior to any metal product. The features of such synthetic fiber ropes can be exemplified by light weightness, high tensile strength characteristics, high elasticity, low moisture absorption, abrasion resistance, incision resistance, chemical resistance, etc. Representative synthetic fiber rope materials include those having trade names of Nylon, Tetoron, Cremona, and Vectran (polyarylate fiber). Furthermore, polypropylene is also used as a synthetic fiber rope material. In particular, Vectran can endure the tensile force equivalent to that applied to a metal wire rope having the same diameter.
The synthetic fiber rope as described above is usable in various ways including, for example, in construction machines such as cranes, buildings and structures such as suspension bridges, and hoisting accessories such as those used for overhead door (over door) for the industry use and for the housing equipment. In order to connect the synthetic fiber rope to an external member or apparatus, in general, it is necessary to attach a clamping part 2 (or a terminal) to a terminal end portion 3 of a synthetic fiber rope 1 as shown in FIG. 1 (FIGS. 1A and 1B). More specifically, the clamping part 2 is a sleeve made of metal. The sleeve is caulked by applying a uniform force N from the outside to the circumferential surface of the sleeve. With the clamping part 2 firmly fixed to the rope 1, when a force F is applied to the other end of the synthetic fiber rope 1, the same amount of force F is generated in the opposite direction (see FIG. 2). If it is assumed that the equilibrium state is maintained, the following relational expression holds as a conceptual theoretical expression.F=μN  (1)
In this expression, μ represents the effective coefficient of static friction between the clamping part 2 and the synthetic fiber rope 1, and N represents the vertical force applied, for example, in accordance with a caulking step.
The following method is available to connect the synthetic fiber rope to the external apparatus. That is, as shown in FIG. 3, a terminal end portion 3 of a synthetic fiber rope 1 is shaped into a “loop” by a clamping member 2 such as a sleeve. The loop portion is connected to a connecting portion of an external apparatus, for example, a hook fixture (or hook metal fixture). When the clamping member 2 is fixed to the terminal portion 3, a method in which the sleeve is caulked as described above is generally used.
Japanese Patent Application Laid-open No. 5-115117 discloses a method in which a wire member formed of twisted wires is inserted into a holding fixture formed with a plurality of helical parts to thereby fix the wire member and the holding fixture to each other. Japanese Patent Application Laid-open No. 5-115117 also describes that a friction enhancing agent may be applied to the inside of the helical parts of the holding fixture. On the other hand, Japanese Patent Application Laid-open No. 5-247862 discloses, as an exemplary conventional method for fixing a metal sleeve and a terminal end portion of a fiber composite soft member, a method in which a thermosetting resin liquid such as those based on an epoxy resin is filled as an adhesive into a space between a metal sleeve and a circumferential surface of the terminal end portion of the fiber composite soft member to impregnate the thermosetting resin liquid into the fiber composite soft member, and then the thermosetting resin liquid is cured to thereby integrally adhere the metal sleeve to the fiber composite soft member. Japanese Patent Application Laid-open No. 2010-43366 discloses a procedure in which a terminal end portion of a rope inserted into a tapered end portion of a metal pipe is impregnated with a curable resin or a viscoelastic gap filler, and a space between the terminal end portion of the rope and the metal pipe is also filled with the curable resin or the viscoelastic gap filler, followed by being cured to form a same shape as that of the taper of the metal pipe around the terminal end portion of the rope.
Japanese Patent Application Laid-open No. 2000-234284 discloses a method for fastening an terminal end portion of a fiber rope in which the terminal end portion of the fiber rope is untwisted (loosened) and inserted into a socket; and a fixing agent or material, prepared by mixing an inorganic powdery material and a thermosetting resin in a predetermined weight ratio, is injected into the interior of the socket and is cured. Japanese Utility Model Publication No. 54-116635 discloses a compression-joining portion of a plastic rope wherein the compression-joining portion is formed by filling rigid particles in a gap or space between a terminal end portion of a plastic rope in which the twist of the plastic rope is untwisted and a sleeve surrounding the terminal end portion, and by compressing the sleeve together with the rigid particles.
Incidentally, the tensile force of the synthetic fiber rope developed in recent years is extremely high as described above. In Vectran, etc. which has a diameter of 4 mmφ, the maximum tensile force F reaches 12 kN (kilonewtons). FIG. 6 shows a result of a tensile strength test performed for Vectran with a loop structure as shown in FIG. 3. As is clearly shown in FIG. 6, a certain proportional elongation is exhibited until the load to Vectran arrives at a certain value. However, when the load arrives at the certain value which exceeds the frictional force between Vectran and the sleeve, the slip phenomenon takes place. This process is repeated, and the maximum value of the tensile force F cannot exceed a certain value any more.
In order to increase the tensile force F, it is conceived that two clamping parts 2 are used in the extending direction of the rope (see FIG. 4). However, according to an experiment performed by the inventors of the present invention, the maximum tensile load value is merely increased 1.5 to 2 times as compared with a case in which one clamping part 2 is used, as shown in FIG. 6 for the result of the tensile strength test. The slip phenomenon still exists, and it is impossible to greatly increase the maximum tensile force F. More specifically, the slip phenomenon takes place at about ⅓ of the maximum tensile force of Vectran when one sleeve is used, and at about ½ of the maximum tensile force of Vectran when two sleeves are used, therefore not possible to sufficiently endure the load and/or the stress exerted by the external apparatus. The phenomenon as described above arises in the same manner not only with Vectran but also any other high tensile force synthetic fiber rope. Currently, there exists no effective method of reliably fixing a clamping member to a terminal end point of a synthetic fiber rope, nor any suitable clamping member. Even though any synthetic fiber rope having a high tensile force is developed, such a rope cannot be utilized as a part of an actual mechanical structure in actual circumstances. In the structures disclosed in Japanese Patent Application Laid-open No. 2000-234284 and Japanese Utility Model Publication No. 54-116635 respectively, it is necessary that the end portion of the rope is untwisted, requiring labor and time, and that thermosetting resin and a large amount of the rigid particles have to be charged inside the sleeve, increasing the cost.